CCR People

Bette Otto-Bliesner, Deputy Division Director and Senior Scientist

Short Bio

Bette Otto-Bliesner is a Senior Scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, and serves as head of NCAR's Paleoclimate Modeling Program.

Born in Chicago, Illinois, Otto-Bliesner first became interested in Meteorology as a child watching P.J. Hoff, the CBS affiliate weatherman. She earned her doctorate in Meteorology in 1980 at the University of Wisconsin - Madison. She worked at NCAR in the General Circulation Modeling group from 1974-1976 and rejoined NCAR in 1995, coming from a faculty position in the Geology Department at the University of Texas at Arlington.

As a nationally and internationally recognized expert in using computer-based models of Earth's climate system to investigate past climate change and climate variability across a wide range of time scales, she has been involved in the IPCC Working Group I reports since the Third Assessment and was a Lead Author for the IPCC AR4 and AR5. She served as the Chair of the International Geosphere-Biosphere Programme (IGBP) Past Global Changes (PAGES) and is currently Co-chair of the Community Earth System Model (CESM) Paleoclimate Working Group. She is a member of the Scientific Steering Committee for the Paleoclimate Modeling Intercomparison Project (PMIP), the group that coordinates international climate model experiments addressing past climate change relevant to understanding future change.

Education

Ph.D., Meteorology, University of Wisconsin-Madison, 1980
M.S., Meteorology, University of Wisconsin-Madison, 1974
B.S. with Honors, Meteorology, University of Wisconsin-Madison, 1972

Current Research Projects

Last Millennium Variability of Climate

The climate of the Common Era before the industrial period provides a baseline for understanding the background of natural climate variability upon which our current anthropogenic change is superimposed. As this period also contains high data density from proxy sources (e.g. ice cores, stalagmites, corals, tree rings, and sediments), the Common Era provides a unique opportunity for understanding not only global but regional-scale climate responses to external forcing. Our studies take advantage of a unique ensemble of CESM simulations that we recently completed and are available to the community. This ensemble includes 38 simulations forced with the transient evolution of solar intensity, volcanic emissions, greenhouse gases, aerosols, land use conditions and orbital parameters, together and individually, for 850-2005.

Our results demonstrate an important influence of internal variability on regional responses of surface temperature and precipitation, ocean circulation, sea ice, and ENSO variability. All the forcings are found to be important for explaining the responses during the preindustrial period, while anthropogenic greenhouse gas and aerosol changes dominate the forced variability of the late 20th century. Collaborative with geologists, statisticians, and social scientists at the University of Arizona and Cornell University, we are using CESM simulations for the Last Millennium, historical period, and future, to understand megadrought risk and convey this knowledge to stakeholders.

Glacial-Interglacial Climates and Abrupt Changes

The coupled ocean-atmosphere-terrestrial ecosystem has undergone dramatic change over the last 21,000 years (kyr) accompanied by large changes in insolation, atmospheric greenhouse gases, continental ice sheets, and meltwater fluxes. Superimposed on the background climate evolution are abrupt climate change events of the North Atlantic region and monsoons-ecosystems. The great magnitude of the signals and the availability of extensive proxy climate records make this period an excellent target for validating state-of-art Earth System Models, such as CESM.

Our CESM simulations have allowed us to investigate the mechanism and feedbacks of deglacial climate change and its interpretation in the data records. Two examples: (1) Much of equatorial Africa suddenly became much wetter ~14,700 years ago, ushering in an "African Humid Period" that continued well into the Holocene. Our CESM results show that a reduction in the Atlantic Meridional Overturning Circulation (AMOC) at the beginning of the last deglaciation caused a reduction in precipitation in northern and southeastern equatorial Africa. When the AMOC became stronger again, wetter conditions developed in response to a combination of increasing greenhouse gas concentrations and strong summer sun. (2) Consistent with most paleo ENSO reconstructions, our model simulates an orbitally-induced strengthening of ENSO during the Holocene. Increasing deglacial atmospheric CO2 concentrations tend to weaken ENSO, whereas retreating glacial ice-sheets intensify ENSO.

CESM, similar to many state-of-art ESMs, simulates climate variables that cannot be compared directly with the proxy variables, leaving a significant uncertainty in model-data comparison. To better compare CESM results, we are finishing a project to have CESM predict water and carbon isotopes as well as other tracers. Next steps are to test the isotope-enabled CESM against proxy observations of the last 21,000 years.

Arctic Warmth and the Greenland Ice Sheet

The Arctic is currently warming at an alarming rate and we do not fully understand why. Nor do we have confident projections of the extent, rates, and thresholds for Greenland ice sheet melting over multiple centuries. The paleo record highlights the susceptibility of ice sheets and sea level to increased Arctic temperatures, even for global warming much less severe than that predicted for future climate. We are combining knowledge from geological and ice core records along with CESM coupled to the Community Ice Sheet Model (CISM) to study the susceptibility of the Greenland ice sheet to greater warming at high latitudes, caused by strong cryosphere-climate feedbacks, for the Last Interglacial (125,000 years ago), Pliocene (~3 million years ago) and long-term future (3000 AD).

For the Pliocene, we are also exploring the interaction among terrestrial feedback mechanisms during the Pliocene - vegetation albedo, atmospheric water vapor, and black carbon emitted from fire - and their roles in amplifying Arctic surface temperatures. High-resolution reconstructions of past temperatures, atmospheric CO2, and fire are being combined with a series of CESM experiments to disentangle how these processes may have been interacting to amplify Arctic temperatures.

Cretaceous Climates

The Cretaceous from 145 to 66 million years ago represents a considerable challenge to our understanding of how the Earth system operates on long timescales. It was characterized by periods of much warmer terrestrial and ocean temperatures than today and dramatic changes in the ocean circulation and biogeochemistry. Atmospheric carbon dioxide, as well as possibly other greenhouse gases, was present in higher concentrations in the atmosphere than present. We are using CESM to assess the control of atmospheric carbon dioxide versus the changing paleogeography in determining the evidence provided in geological records. Our results are being compared to those of the HadCM3 models to test the robustness of our results.

At the end of the Cretaceous there was a mass extinction event when many non-avian dinosaurs and other animal groups died out. It coincides in the fossil record with a soot and dust debris layer containing Iridium pointing to a large asteroid impact as a possible cause of the extinction. We are using the Whole-Atmosphere Community Climate Model (WACCM), a three-dimensional high-top climate model with interactive ocean, sea ice and chemistry, plus explicit aerosol calculations from the Community Aerosol and Radiation Model for Atmospheres (CARMA), to explore the long-term effects of the Chicxulub impact.